Re: [PATCH net] net: spacemit: Hold RTNL lock in emac_resume() and emac_suspend()

From: Vadim Fedorenko <vadim.fedorenko@linux.dev>
To: Breno Leitao <leitao@debian.org>, Ali Tariq <alitariq45892@gmail.com>
Cc: netdev@vger.kernel.org, Andrew Lunn <andrew+netdev@lunn.ch>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Yixun Lan <dlan@kernel.org>,
	Troy Mitchell <troy.mitchell@linux.spacemit.com>,
	Vivian Wang <wangruikang@iscas.ac.cn>,
	Chukun Pan <amadeus@jmu.edu.cn>,
	Siddharth Vadapalli <s-vadapalli@ti.com>,
	Tomas Hlavacek <tmshlvck@gmail.com>,
	Muhammad Bilal <meatuni001@gmail.com>,
	Maxime Chevallier <maxime.chevallier@bootlin.com>,
	"open list:RISC-V SPACEMIT SoC Support"
	<linux-riscv@lists.infradead.org>,
	"open list:RISC-V SPACEMIT SoC Support"
	<spacemit@lists.linux.dev>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net] net: spacemit: Hold RTNL lock in emac_resume() and emac_suspend()
Date: Thu, 5 Nov 2026 23:28:31 +0100	[thread overview]
Message-ID: <6c36ec6d-5bc8-4ac3-8ad0-79eac7873b67@linux.dev> (raw)
In-Reply-To: <auyG7hGJtMzV0Gbi@gmail.com>

On 05/11/2026 13:40, Breno Leitao wrote:
> On Thu, Nov 05, 2026 at 05:34:37PM +0500, Ali Tariq wrote:
>> The emac_resume() calls the emac_open() and emac_suspend() calls
>> emac_stop() functions directly without holding the lock through
>> rtnl_lock(). These functions rely on phy_disconnect() which reads pointer
>> with rtnl_dereference(). But since no lock is being held,
>> rtnl_dereference throws a suspicious RCU usage on
>> Orange Pi RV2 (SpacemiT K1) warning when lockdep is enabled.
>>
>> WARNING: suspicious RCU usage
>> drivers/net/phy/phy_device.c:1831 suspicious rcu_dereference_protected() usage!
>> Call Trace:
>> phy_detach_internal+0x490/0x5f2
>> phy_disconnect+0x90/0xc0
>> emac_stop+0x114/0x626
>> emac_suspend+0xac/0x126
>> platform_pm_suspend+0x72/0xe4
>>
>> Hold RTNL lock before emac_open() and emac_stop() with rtnl_lock() and
>> release the lock when functions return with rtnl_unlock().
> 
> This would work, but I am wondering if it would be possible to call rtnl
> inside the _open function, when dealing with the PHY? in other words,
> shrink the time rtnl is held.

+1, especially in emac_open() rtnl is needed only in error path case